Framing modifications

[live4ever]

I’m doing some basic seismic retrofitting, insulating, and drywalling of our garage located under our home, which is also my shop.  The home is late 1930s.  Since all the framing is currently exposed, I’m taking the opportunity to also stiffen the bouncy floor above, and modify framing to shore up weak spots...eg repair herringbone struts. 

My question concerns some existing framing that I don’t know the term for but have always wondered about.  These are 45 degree supports made from 1x6 that connect floor joists above to wall studs below.  Originally they were located on every other joist/stud, but one side of the house has seen most of them cut/removed over the decades I assume for plumbing/electrical  projects.  What exactly is the function of these supports and how effective are they?  I assume they partly support the joists somewhat reducing the effective span, and also prevent twisting of the joist?  Since they take up a decent amount of headroom and also present drywall challenges, I’m wondering about removing them, but replacing their “function” with the appropriate measures.  Thoughts?

 

[Bob D.]

Just for clarification, that photo should be rotated clockwise 90 degrees correct?

Never run across anything like that here 3000 miles away but building methods
differ greatly especially when the structure was built before there probably was
a building code.

Maybe part of the problem you are having now is because some of these braces
were removed in the past.

 

[rizzoa13]

That's rack bracing like you would see on the underside of some two story decks. I've never seen it in a house but if it was on every other joist I'd assume when it was built that the house was specced with them in mind. Ie I wouldn't remove them. Sorry I can't be of more help.

 

[live4ever]

Thanks guys.  Yeah rizz I agree it seems, based on the fact these are 1x’s and land on either side of the joist and stud, that the purpose of these is sway/rack bracing as opposed to any meaningful joist load support.  I am adding H10ARs to every joist, which I believe should provide at least the same shear and uplift resistance as these, if not significantly better.  I thought I’d ask in case some have run across this before and what common practice is, but maybe this technique was rarer.

 

[bkharman]

Is there a hole in the middle of those 1x boards?  Reason I ask is that my first house in the states was a 1930’s Craftsman and the basement had those same boards. The hole was for a chin-up bar that had been removed some time ago. I stored lumber above it like you have the clamps.

Cheers. Bryan.

Edit:  sorry, I completely missed the point that there used to be many more of the braces.

Sent from my iPhone using Tapatalk

 

[live4ever]

Is there a hole in the middle of those 1x boards?  Reason I ask is that my first house in the states was a 1930’s Craftsman and the basement had those same boards. The hole was for a chin-up bar that had been removed some time ago. I stored lumber above it like you have the clamps.

Cheers. Bryan.

Edit:  sorry, I completely missed the point that there used to be many more of the braces.

Sent from my iPhone using Taps talk

Hehe, no holes for chin-up bars.  Yeah they do make for a nice little niche for storing long things, like extra molding or rarely used pipe clamps.  I will miss all the storage nooks and crannies I’ve had with the walls bare, but the truth is I was just collecting clutter and scraps anyways.  Like you see in the photo...never know when I might need 2x4 offcuts!  Sheesh.

 

[live4ever]

Just for clarification, that photo should be rotated clockwise 90 degrees correct?

Not sure what you’re seeing but on my computer the thumbnail is rotated 90 degrees but the photo opens in the correct orientation.  For reference, that’s the top of my drill press, which last I checked is still standing upright.

 

[Bob D.]

Nope, for me both the thumbnail and the full size image are rotated CCW 90°.

Too bad there is not a way to rotate images after uploading to the forum. So
many different pieces or hardware not to mention the various software packages
out there for post-processing of images that are inconsistent in how they handle
images, not to mention the different file formats that it must be difficult for any
forum software to handle them all without a few glitches. But having the ability
to rotate the image in the forum software after uploading would solve all that.

It's not just here, I've seen it on other forums too over the years.

I'm getting tired of flipping my monitor on it's side.

 

[Naildrivingman]

I don't see any purpose to those diagonal braces. Any strength they would lend is strictly borne by fasteners.  Possibly they were temporary bracing that never got removed after construction or they were just somebody's idea of a good thing.  IMO they neither help nor hurt the current situation.

 

[Gregor]

How are the individual floor joists anchored to the floor?

Asking because the 45° braces could well be designed to keep the angle between the floor joists and the ceiling beams at the intended (right) angle (keeping the floor joists upright) to prevent the construction from turning parallelogram (= the construction leaning to one side and subsequently collapsing).

 

[Michael Kellough]

"Any strength they would lend is strictly borne by fasteners."

In this application the fasteners work in shear and are very strong.

"I am adding H10ARs to every joist, which I believe should provide at least the same shear and uplift resistance as these"

First, will the notch is those plates fit those old joists?
Second, used as designed those plates provide racking/shear resistance perpendicular to the support the wooden braces are providing. They are not a replacement.
Simple flat plates with holes would be more suitable (shear resistance in right direction) but may not be sufficient to replace the long 45* brace.

I think you should consult a local engineer since you are in earthquake area and your house is sitting on top of that structure.

 

[live4ever]

I've spent a few weeks researching this all in-depth and without getting into a really long discussion about seismic retrofitting and old SF Bay Area houses - not really relevant to most of you - the long and short of it is yes, those diagonal braces are originally designed to resist racking or swaying.  The members operate in tension.

Here's what else I learned:
In general, based on what was learned about HOW houses fail in major earthquakes (thanks to Northridge 1994 and Loma Prieta 1989), they're considered dispensable if they are in the way of other more important seismic retrofits.  So for example, it's far more important to retrofit in a proper shear wall than have that compromised by the existing diagonal braces.  The strengthening that the shear wall offers is far more relevant to how houses die in earthquakes, namely shear forces along the foundation (addressed by anchoring the mudsill, installing plywood, and shear tension ties along the joists and blocking).  I'll be removing the diagonal braces where I'm adding proper shear walls and where additional stiffening walls are being placed. 

Michael - the H10AR is the 2" version of the regular H10A, intended for older lumber.  I actually have a handful of joists that are even a touch thicker than that, maybe 2-1/8".  But based on the engineering calculations it's vastly overkill to put one on each joist - I can skip one here and there, and in a few cases, I also have plumbing obstructions at the top plate that prevent being able to nail or screw these in. 

 

[Michael Kellough]

Glad you've done the research.

 

[live4ever]

Glad you've done the research.

Seismic retrofitting is a black hole of doom.  Living in earthquake country could also be considered the same... [scared]